Electron discharge device



ELECTRON DISCHARGE DEVICE Birger Eiane, Horseheads, N.Y., assignor to Westinghouse Electric Qorporation, East Pittsburgh, Pin, a corporation of Pennsylvania Filed Jan. 28, 1957, Ser. No. 636,611

7 Claims. (Cl. 315-35) This invention relates to devices for amplifying high frequency electric waves, and more particularly, to those devices known as traveling wave tubes.

In general, a traveling wave tube is based upon the principle of interaction between a traveling electric field and an electron beam traveling at about the same velocity. In a typical traveling wave tube, the electron beam is guided by electric and magnetic fields through a conductive helix which is coupled to input and output wave guides. The input signal produces an axially directed electric field, or wave, in the space surrounded by the helix. The electron beam is concentrated and guided by an axial magnetic field created by magnetic coils or permanent magnets which surround the helix on the outside of a glass envelope which, in turn, encloses the helix. The magnetic structure may include pole pieces for an induced magnetic field.

In prior art devices, the magnetic beam-control coils were located outside the envelope because they were heavy and bulky. Also, ordinary permanent magnets cannot be used inside a vacuum envelope for a number of reasons. Ordinary permanent magnets may not retain their magnetization during the heating and baking operations which are required in the manufacture of such a device. Also the ordinary permanent magnet is a conductor which may become inductively heated during manufacture and operation of the tube. The conductive permanent magnets also have eddy currents which tend to negate their magnetic efficiency. In addition, these con- 7 ductive permanent magnets have a higher vapor pressure than desirable in many applications. In a traveling wave tube, a conductive permanent magnet may not be used as a support for the helix itself because it will short across the turns of the helix. If the permanent magnets are located outside the tube envelopes, a support structure is necessary for the helix which, in turn, necessitates a larger and more expensive magnet because of the larger center 'space required. For these reasons, prior art traveling wave tubes frequently weighed as much as 30 to 40 pounds including the focusing coils, took up a considerable amount of space and were quite expensive.

In my invention, non-metallic permanent magnets are placed inside the tube envelope and act as both magnetic focusing coils and as part of a support structure for the helix. In this way, the weight of the traveling Wave tube is reduced from about 30 to 40 pounds to less than one pound in some cases and the bulk and expense are also reduced considerably. In addition, with the magnet assembly within the tube envelope, the assembly and application of traveling wave tubes in the field is considerably simplified.

Therefore, it is an object of this invention to provide :an improved traveling wave tube.

It is another object of this invention to provide an improved magnetic beam-control structure for a traveling wave tube.

It is a further object to provide an improved magnetic United States Patent 2,939,994 Patented June 7, 1960 beam-control structure and helix support structure for a traveling wave tube.

It is an additional object to provide an improved magnetic beam-control structure for a traveling wave tube using a non-metallic permanent magnet material.

These and other objects of my invention will be apparent from the following description taken in accordance with the accompanying drawings throughout which like reference characters indicate like parts, which drawings form a part of this application and in which:

Figure l is a prior art traveling wave tube with some parts broken away and some parts in section;

Fig. 2 is a sectional view of a portion of the traveling wave tube showing the magnetic beam-control structure and hel x support structure according to one embodiment of my invention;

Fig. 3 is a sectional view of a portion of a traveling wave tube similar to that shown in Fig-2 according to another embodiment of my invention;

Fig. 4 is a sectional view of a magnetic beam-control coil and helix support structure incorporated in a traveling wave tube according to still another embodiment of my invention; and

Fig. 5 is a sectional view of a portion of a traveling wave tube similar to that shown in Fig. 4 according to another embodiment of my invention.

Referring now particularly to Fig. 1, there is shown a.- traveling wave tube of the typeadapted to be used as an amplifier for ultra high frequencies. An electron beam tube is shown including an envelope member 11 made of glass or similar material including an elongated portion 13 which is of uniform diameter along its length. The elongated portion 13 is connected to an enlarged electrode portion 15. In the enlarged electrode portion 15, there is provided a suitable means for producing an electron beam such as an electron gun of the type known as 3. Pierce gun which is described in the book Traveling-wave Tubes by I. R. Pierce, D. Van Nostrand Co., Inc. 1950) After the electron beam is generated by the electron gun, it goes through a metallic cylinder member 17 which has a configuration which will provide suitable electric field patterns and is biased to a positive potential in order to-accelerate and focus the electron beam. The electron beam travels through a conductive helix member 19 and 'is further concentrated and guided along an axial path within the helix member 19 by magnetic beam-control means comprising a magnetic focusing coil member 21 and a cylindrical coil member 23. The strong magnetic field formed by the cylindrical coil member 23 also serves to prevent the deviation of the electron beam from the desired path by outside magnetic influences. The electron beam is collected at the other end of the helix 19 by an anode electrode 25.

In the operation of the device, the metallic focusing cylinder member 17 and the helix member 19 are maintained at a potential at the order of 1500 to 2000 volts above that of the cathode by a potential source which may be conventionally represented by a battery 27. The anode electrode 25 is maintained at a somewhat lower voltage for the purpose of decelerating the electron beam before it strikes the anode electrode 25. An ultra high frequency signal is applied to the helix at the point of entry of the electron beam into the helix 19 and a larger signal of the same frequency appears at the opposite. or output end of the helix 19. The ultra high frequency current flows around the helix 19 thereby producing in the center of the helix 19 an axially directed ultra high frequency field which travels longitudinally at a phase velocity slower than the speed of light by a factor called the pitch factor of the helix 19. The pitch factor is the ratio of length of wire around the helix 19 to the axial r and an output coupling member 37.

portion of the helix member 19.

length between 'any' two'axial points. Therefore, with proper choice of the pitch factor, the traveling wave can be given a phase velocity about the same as the velocity of the electrons in the beam. For example, if the beam consists of 1500 volt electrons, the corresponding pitch factor will be about 13. In this example, the wave length of'the high. frequency wave is about 8 millimeters whereas the useful portion of the helix' may be from 30 to 50 centimeters long. Therefore, it is seen that the electrode distance may be many wave lengths of the useful propagating wave.

If the electrons are traveling faster than the ultra high frequency field they can deliver power to the ultra high frequencycircuit. If the electrons are traveling slower than the ultrahigh frequency field, they will accept power'from it. The most effective interaction occurs when there is only ,a relatively slight difference between the two speeds.

' Ordinarily, the traveling wave tube is intended for the uniform amplification ofawide band of high frequency waves andthe high frequency portions of the device must necessarily have dimensions suitable for use at the particular wave length to be amplified. At the input end of the helix .19, there is located an input coupling member supportsection 31 which supports an input coupling member 33. At the output end of the helix 19 there is located a similar output coupling support section 35 The input coupling member support section 31 and the output coupling member support section 35 are positioned in spaced rela- 'tionship t'o the metallic cylinder member 17 and the anode electrode 25 by a ceramic spacer member 39, non- -conductive helix rod support'members 29 and a ceramic 47 is coupled to a source of signal energy so'as to produce a mode of wave propagation having an electric field vector parallel to the input coupling 33. A corresponding wave is thus generated along the coupling strip and is imparted to the helix member 19 through the input impedance matching section 43. This input impedance matching section 43 acts as a tapered transmission line and transfers the wave form from the relatively high impedance at the end of the coupling strip to the relatively' low impedance:of. the helix 19 with a main reflection of energy. back" to the signal source. The initial interaction between the traveling wave and electron beam is very slight as the wave serves initially only to produce waves of charge density and velocity in the electron beam. However, as the wave and electron beams travel along the axis of the helix member 19 and as a wave is established in the'electron beam, a condition is established in which the wave travels a little slower than the electrons forming the'modulated electron beam and'the electrons impart energy to'the wave in a manner which increases the amplitude of the wave at a rapidly increasing rate. As the amplified wave reaches the output end "spacer member 41. The helix member 19 is joined to a the input coupling member 33 by the input impedance matching section '43 and the output coupling member 37 isjoined to the helix member 19 by the output impedance 7 ,fe'rence of the helix member 19 to provide a .wave trans missionpathof uniformly changing impedance from the relatively high impedance at the end of the coupling member to the relativelylowimpedance of the center In order to utilize the device in there is provided an incoming wave path which may be represented by an input wave guide 47, into which the input'wave signal, to be amplified is introduced. An output wave path which may be represented by an output wave guide 49 transfers the amplified output wave to the load circuit. A wave resonator 51 is coupled to a conductor member 53 in order to prevent the radiation of high frequency energy which is imparted to the con.- ductor 53 by the helix member 19. The input and output wave guides 47.and 49 are joined by the metallic cylindrical member 55 and are also connected electrically to the metallic shell'member 57 of the magnetic focusing coil member 21 and the wave resonator 51 to provide,

in effect, the outer conductor of a concentric transmis- V sion line. The input coupling member support section 31, in conjunction with the metallic shell member 57 of the magnetic focusing coil member 21 and the wall .of'the input wave guide 47, forms an open-circuited transmission linewhich is electrically one-quarter the ,length of the wave length to be amplified. It thus acts asa low impedance path across the opening in the wall of the waveguide in which the envelope member 11 is insertedjand also acts as a low impedance support point for the input coupling member 33. The output coupling member support section 35 cooperates with the walls of the wave resonator 51-and the output wave guide 49in a'similar manner to provide a low impedance support point for the output coupling member 37. In the operation of thedevice, the input wave guide an operable system,

of the helix member 19, it traverses the output impedance matching section 45 and is transferred to the output wave guide 49 by means of the output coupling member 37. a

In Fig. 2 there is shown a portion oftraveling wave tube according to one embodiment of my invention including an elongated portion of an insulative low loss envelope member 59 made of a suitable material such as glass or quartz or the like which encloses ahelix member 19. Aninsulative ceramic tube 61 serves as the helix support member which in turn is supported by a plurality of non-metallic permanent magnet members 63. Also if desired, pole pieces 62 may be utilized to concentrate the magneticfield in certain configura-- tion. Of course, our invention is not restricted to the helix support member 61 or permanent magnet member 63 of the particular, configuration shown. As can be seen, the permanent magnetic members 63 surround the helix member 19 and are located between the helix member 19 and the envelope member 59. In this particular embodiment, the envelope member 59 supports the magnet members 63. I a l a a These permanent magnetic members 63 may be made of a material such as that having thechemical'formula BaO.6Fe 0 This material is non-metallic and insulative but is a ceramic-likepermanentfmagnet material having a 'highcoercive force. Thismaterial has a high thermal stability and'excellent resistance to demagnetization influences. The material'has the property thatit may'b'eheated to high temperatures and lose some of its magnetic properties but upon cooling to normal temperatures it is found that it regains them. This material also has a high specific resistance which makes it particularly adaptable for use in ultra high frequency devices. The specificgravity of this material is approximately 4.5 compared to approximately 7.5 for most magnet steels, whichhas the additional advantage of providing a comparatively light material for use in a traveling wave tube. Other materials which possess similar magnetic properties and which may 'be used in our V 085, and which is assigned to thesame assignee as the subject application. If desired, other binder materials, such as silicates or ceramic materials may be used in place of' the binder materials disclosed in the Cornish application. The helix support member 61 may be made of a ceramic material such as alumina (A1 Quartz or other low dielectric loss materials may alsobe used.

In Fig. 3 there is shown a portion of a traveling wave tube similar to that shown in Fig. 2, including an insulative envelope member 59 and a helix member- 19, which is supported directly by a plurality of permanent magnetic members 65 rather than by the helix support member 61 of Fig. 2. In this embodiment, as well as that shown in Fig. 2, pole pieces 62 may be desirable in some instances to aid in concentrating the magnetic field. The particular embodiment shown in Fig. 3 may be suitable at comparatively low frequencies at which a more rugged helix may be used. I

In Fig. 4 there is shown a traveling wave tube according to a different embodiment of our invention in which an insulative envelope member 59 encloses a helix member 19 and a helix support member 61 which,,in turn, is surrounded by a permanent magnetic member 69. In this case, the permanent magnet member 69 is of the same material as it is in Figs. 2 and 3 but is in the form of a one-piece tube rather than in a number of permanent magnets. A permanent magnet of this type may be magnetized before insertion into the traveling wave tube or it may be found to be desirable in some circumstances to magnetize the magnet member 69 after it has been inserted into the traveling wave tube.

In Fig. 5 there is shown another embodiment of a portion of a traveling wave tube somewhat similar to that shown in Fig. 4 in which the helix member 19 is directly supported by a non-metallic permanent magnet member 69 which is enclosed in an insulative envelope member 59. g

It is understood the helix support member 61 shown in Figs. 2 and 4 and the permanent magnet members 63, 65 and 69 shown in .Figs. 2, 3, 4 and 5, may be made in other configurations without departing from the spirit and scope of my invention. For example, the helix support member 61, shown in Figs. 2 and 4, may be replaced by members similar to the non-conductive helix rod support members 29 shown in Fig. 1. The rod-like support members 29 tend to reduce dielectric loss.

These permanent magnet members 63, 65 and 69 may be magnetized to form an alternating field if desired either before or after insertion into the traveling wave tube and after insertion into the tube, may be processed in the normal baking cycle for the vacuum tube. As the magnetic materials used in this invention are insulators, they do not interfere with the electric field requirements to the same extent as metallic magnet members and pole pieces and therefore may be placed closer to the helix itself which results in a lighter structure. Also, these non-metallic permanent magnets may be magnetized in desirable three-dimensional configurations and the choice of patterns with magents of this type is greater and much simpler than with pole pieces. Also, the magnetic structure of a tube of this type may be changed even after it is completed which may have desirable advantages.

Although the present invention has been shown in a few forms only, it will be obvious to those skilled in the art that it is not so limited but is susceptible of various changes and modifications without departing fi'om the spirit and scope thereof.

I claim as my invention:

1. An electron discharge device including an elongated envelope member, wave-conducting means including a conductive helical member within said envelope, said wave-conducting means having an input end and an output end, means within said envelope to direct an electron beam axially into said helical member, means to impress waves to be amplified upon said input end so that said waves may travel along said wave-conducting means and interact with said electron beam so that said waves are amplified, means to remove said amplified waves from said output end and magnetic beam-control means including at least one magnet member positioning said helical member within said envelope member, said magnet member being comprised of a non metallic permanent magnet material.

2. An electron discharge device including an elongated envelope member, wave-conducting means including a conductive helical member within said envelope," said wave-conducting means having an input end and an output end, means within said envelope to direct anelectron beam axially into said helical member, means to-impress waves to be amplified upon said input end so that said waves may travel along said wave-conducting means and interact with said electron beam'so that said waves are amplified, means to remove said' amplified waves from said output end, a tubular insulative helix support member surrounding said helical member, and magnetic beam-control means including at least one magnet member unit positioning said support member within said envelope member, said magnet member being comprised of a non-metallic permanent magnet material.

3. An electron discharge device including an elongated envelope member, Wave-conducting means including a conductive helical member within said envelope, said wave conducting means having an input end and an output end, means within said envelope to direct an electron beam axially into said helical member, means to impress waves to be amplified upon said input end so that said waves may travel along said wave conducting means and interact with said electron beam so that said waves are amplified,,meaus to remove said amplified waves in said output end, and magnetic beam-control means including a tubular magnet member surrounding said helical member, said tubular magnet member positioning said helical member within said euvelopemember, said tubular magnet member being comprised of a non-metallic permanent magnet material.

4. An electron discharge deviceincluding an elongated envelope member, wave-conducting means including a conductive helical member within said envelope, said wave-conducting means having an input end and an output end, means within said envelope to direct an electron beam axially into said helical member, means to impress waves to be amplified upon said input end so that said waves may travel along said wave-conducting means and interact with said electron beam so that said waves are amplified, means to remove said amplified waves from said output end, a tubular insulative helix support member surrounding said helical member, and magnetic beamcontrol means including a tubular magnet member surrounding said support member, said magnet member positioning said helical member within said envelope member, said magnet member being comprised of a nonmetallic permanent magnet material.

5. An electron discharge device including an elongated envelope member, wave-conducting means including a conductive helical member within said envelope, said wave-conducting means having an input end and an output end, means within said envelope to direct an electronbeam axially into said helical member, means to impress waves to be amplified upon said input end so that said Waves may travel along said wave-conducting means and interact with said electron beam so that said waves are amplified, means to remove said amplified waves from said output end, and magnetic beam control means including a plurality of magnet members positioning said helical member within said envelope member, said magnet members being comprised of a non-metallic permanent magnet material.

6. An electron discharge device including an elongated envelope member, wave-conducting means including a conductive helical member within said envelope, said wave-conducting means having an input end and an output end, means Within said envelope to direct an electron beam axially into said helical member, means to im- Tpress. wavesto'ibelamplified upon said iiiputfl eiadi so that said waves/may rtravel, along said waye-confi ictipg means pdsitionilig said support; member within said envelope @member, j said magnet; members a. beinggconiprised of' a nonmetallic permanent magnet material; j

7.111 1 eleetrqiz discharge deviee including ari eiongateci Y "envelopemem ber, Vwave-condpcting means including" 211' gonducfgive helieal. member within said ,envelope, said wave-ebiidueting means having an iiiput end and admitput eiid, means'within said envelqpe to direct ail'electron beam'axilly into said helieal member, means 'to impress waves' to'be amplified upon said input end so that said waves may trayel along said wave-conducting means and interact: with said electron beam so that said waves are 7 amplified, means to remove said amplified waves from SBid'OliiLPllii endQaiid magnet beam-contrcl means' inbinding at least One magnet me nber positioning said V heiieal me'grihe'r' within saidenvelope'meplbeflsaid magneimemb'er i eing comprised of a non-met-ailic ierm'afiem magnet material selected from the group. consisting of biSmuthide 1': I V H M J j lief ei'ehees Cited iii the file of thispat entf f UNITED STA TESPATEN TS'.

France' May 26; 1954 

